Within the framework of the present application, “friction clutch” is understood to mean in particular a friction clutch which is situated in the drivetrain of motor vehicles driven by an internal combustion engine, between the combustion engine and a transmission, which enables driving off as well as changing the gear ratio, and which for technical reasons is only possible when the traction force is interrupted.
Such friction clutches have an input part and an output part, and transmission of power increases depending on actuation, starting from a completely disengaged actuating position in which essentially no power is transmitted between the input and output parts, all the way to a completely engaged actuating position in which transmission of power between the input and output parts is essentially complete, where transmission of power between the input and output parts occurs by frictional engagement. Conversely, starting from a completely engaged actuating position, in which transmission of power between the input and output parts is essentially complete, all the way to a completely disengaged actuating position, in which essentially no power is transmitted between the input and output parts, depending on actuation a decrease in power transmission occurs.
Such friction clutches are also implemented as dual clutches, and then on the combustion engine side have an input part and on the transmission side a first and a second output part, each of which includes a clutch plate. With a dual clutch, the input part on the one hand and the first output part and/or the second output part on the other hand can be connected with each other or separated from each other. Furthermore, during the transition of a gear change, a flow of power from the input part can be transferred from the first output part to the second output part and vice versa.
It is known to actuate such friction clutches automatically by means of an actuator device, which includes at least one electrical or hydraulic actuator. The actuator device is usually controlled by means of a control device based on characteristic curves and/or parameters which are stored in the control device, and/or which are made available by means of sensors.
The friction clutch can disengage under spring loading and engage by means of the actuating device, or conversely can engage under spring loading and disengage by means of the actuating device. The actuating device can be operated using pressure or tension.
The thickness of the clutch lining is usually designed for the life of a vehicle. In the case of increased wear and early erosion of the lining, the point at which the limits of the lining has been reached is not noticed until the lining has completely worn down, for example acoustically by a scraping rivet of the clutch plate or by lack of torque capacity of the clutch. As a rule, early diagnosis is only possible by means of disassembly and visual inspection, and this is too complicated and too expensive for merely determining the thickness of the clutch lining.
A device which enables simple evaluation and works reliably to detect the operating condition of a friction lining on a friction lining carrier, in particular in the environment of a motor vehicle, is disclosed by DE 10 2007 061 266 A1. There, it proposes to provide at least one olfactorily active substance for recognizing the operating condition of the friction lining. However, the precision with which the operating condition of the friction clutch can be determined using this device depends upon how precisely the olfactorily active substance is situated in or on the friction lining, and how precisely the olfactory information is evaluated.
The descriptive introduction to DE 10 2007 061 266 A1 also mentions a mechanical structure for determining clutch plate wear, as well as an indication of wear by means of electronic sensors. It is also mentioned that wear of friction linings can be determined from a model calculation, by totaling up the energy introduced into the friction system over its operating life and deducing the present operating condition of the friction lining in connection with experimentally determined data on the wear of a friction lining. However, these types of wear determination are either very complex, or do not satisfy elevated demands for precision.